In recent years, a big-screen display device and a TV receiver which use a transmissive liquid crystal panel have spread rapidly. The transmissive liquid crystal panel needs an illuminating device (so-called backlight) which illuminates the transmissive liquid crystal panel from behind. With upsizing of the liquid crystal panel, the illuminating devices are also getting larger, and the number of the light sources (straight-tube type discharge lamps) used have continued to rise. However, if the number of the discharge lamps is increased, power consumption of the illuminating device is also increased, and, as a result, power consumption of the display device with a liquid crystal panel and a illuminating device, and the TV receiver are also increased. Meanwhile, although it is necessary to reduce the number of the discharge lamps which are used so as to reduce the power consumption of the illuminating device for a liquid crystal panel, if the number of the discharge lamps is simply reduced, unevenness in brightness becomes large, whereby image quality is degraded.
So, in the prior art, an illuminating device for a liquid crystal panel which can suppress unevenness in brightness while reducing the number of the discharge lamps is disclosed (see, Japanese Patent Application Laid-Open No. 2005-24746. Hereinafter, called Patent document 1.). In the illuminating device for a liquid crystal panel, two reflecting mirrors each of which has a semi-elliptical surface in cross-section are provided alongside each other in such a way that each other's ones of the focuses overlap each other, and light sources (discharge lamps) are disposed at the other focuses, whereby light reflected by each reflecting mirror forms an image of the light source at the overlapped one focuses, which makes believe as if another light source exists between the two light sources.
However, in the prior illuminating device for a liquid crystal panel of Patent document 1, since it is necessary to dispose a discharge lamp, which is a light source, at a position of one focus of the reflecting mirror, it is necessary to secure a certain amount of distance between the reflecting mirror and a diffuser plate which is disposed in front of the reflecting mirror. As a result, there is a problem that a thickness of the illuminating device is increased.